Preheat over to 350 degree. Cut 6 large hearts out of parchment paper about 14 inches wide.

Place 1 piece of fish in center of 1 side of parchment paper heart. Spread 1 tablespoon tomato butter on fish. Season with salt and pepper. Top with 3 slices tomato and 2 slices onion. Sprinkle with chopped cilantro. Repeat with remaining ingredients.

Fold extra sides of parchemtn hearts over fish. Starting at the top, crimp edges of parchemtn, tucking as you go. Fold end of parchment at elast 3 times, and tuck under fish secure. Place parchment packets on a rimmed baking sheet.